Evaluation of five commercial assays for the detection of anti-dsDNA antibodies: three Crithidia luciliae indirect immunofluorescence test kits and two enzyme immunoassay kits.

OBJECTIVE There are various methods for anti-dsDNA detection. Crithidia luciliae indirect immunofluorescence test (CLIFT) and enzyme immunoassay (EIA) are the most commonly used at present. A number of CLIFT and EIA kits are commercially available. The objective of the present study was to evaluate the diagnostic performance of three commercial CLIFT kits, two commercial EIA kits, and their combinations for anti-dsDNA detection. MATERIAL AND METHOD One hundred thirty nine sera sent for anti-dsDNA testing were investigated. Three commercial CLIFT kits (kit C1, C2, and C3) and two commercial EIA kits (kit E1 and E2) were evaluated. Sensitivities and specificities were calculated. The gold standard methods were the consensus results of all five kits, together with the clinical diagnosis when the results of five kits were discrepant. RESULTS Of 139 sera investigated, 94 (67.6%) sera showed concordant results for all five kits and 45 (32.4%) sera showed discordant results. Thirty-five of those 45 patients (77.7%) were diagnosed as SLE. Sensitivities and specificities of the kits were as follows, Cl 82.1% and 94%, C2 46.4% and 100%, C3 78.6% and 98.8%, E1 71.4% and 94%, and E2 75% and 93.8%, respectively. Kit C3 yielded the maximum sum of sensitivity and specificity (177.4%). Sensitivities and specificities of the combinations of CLIFT and EIA kits were as follows, C1 + E1 89.3% and 90.4%, C1 + E2 98.2% and 87.9%, C2 + E1 73.2% and 94%, C2 + E2 82.1% and 92.8%, C3 + E1 85.7% and 94%, and C3 + E2 94.6% and 91.6%, respectively. The combination of kit C3 and E2 yielded the maximum sum of sensitivity and specificity (186.2%). CONCLUSION Kit C3 was the assay of choice for anti-dsDNA detection. EIA kits yielded lower sensitivities and specificities than two of three CLIFT kits. Therefore, they should not be used as the first assay for anti-dsDNA screening. When CLIFT and EIA assays were combined, sensitivities were increased Kit E2 helped CLIFT kits to detect more SLE cases than E1.